Conventionally, most electronic devices should be connected with power sources to acquire electric power in order to be normally operated. Generally, all of these electronic devices may be plugged into corresponding power sources (for example power sockets) to acquire the electric power through power cables. With increasing development of science and technology, a variety of electronic devices are developed toward small size, light weightiness and easy portability in order to comply with the users' requirements. Although the electronic device can be easily carried, the electronic device cannot be connected with the power source to acquire the electric power through the power cable at any time. Generally, a built-in chargeable battery is usually installed in the electronic device for providing sufficient electric power to the electronic device.
For example, in case that the electricity quantity of the chargeable battery of the electronic device is insufficient, the chargeable battery of the electronic device may be charged by a charging device. In this context, the charging device is also referred as a power transmission device. Generally, the conventional power transmission device has a connecting wire. After the connecting wire is plugged into the electronic device and the conventional power transmission device is connected with the power source, the electric power may be transmitted from the power transmission device to the electronic device through the connecting wire. However, the applications of the power transmission device during the charging process are usually restricted by the connecting wire. For example, since the length of the connecting wire of the power transmission device is limited, the electronic device cannot be operated according to the usual practice or the electronic device cannot be arbitrarily moved. On the other hand, if the conventional power transmission device has been repeatedly used to charge the electronic device for a long term, the connector of the connecting wire of the power transmission device is readily damaged because the connector of the connecting wire is frequently plugged into and removed from the electronic device. Under this circumstance, the charging efficiency of the connecting wire of the power transmission device is deteriorated. If the connector is seriously damaged, the charging task fails to be done through the connecting wire.
With increasing development of a wireless charging technology, a wireless power transmission device for wirelessly charging the electronic device has been introduced into a market in order to solve the drawbacks of using the connecting wire by the wired charging technology. FIG. 1 schematically illustrates the relationship between a conventional wireless power transmission device and a conventional electronic device. As shown in FIG. 1, the conventional wireless power transmission device 1 comprises a main body 10, a power cable 11, a driving circuit 12, and a transmitter coil 13. In addition, the conventional electronic device 2 comprises a casing 20, a receiver coil 21, and a chargeable battery (not shown).
In the conventional wireless power transmission device 1, the power cable 11 is exposed outside the main body 10 in order to be connected with a power source (not shown). Both of the driving circuit 12 and the transmitter coil 13 are disposed within the casing 10. Moreover, the driving circuit 12 is connected with the power cable 11 and the transmitter coil 13. When the driving circuit 12 is driven by the power source, a voltage is provided to the driving circuit 12 and thus an electric current is generated by the driving circuit 12. When the electric current flows through the transmitter coil 13, an electromagnetic effect is generated. According to the electromagnetic effect, a magnetic flux is generated by the transmitter coil 13. In the conventional electronic device 2, the receiver coil 21 is disposed within the casing 20 for receiving the magnetic flux from the transmitter coil 13, so that the magnetic flux is converted into an electric power. The chargeable battery is connected with the receiver coil 21 for storing and utilizing the electric power which is received by the receiver coil 21.
For achieving a power-saving purpose, the conventional wireless power transmission device 1 may be selectively operated in a charging mode or a detecting mode. When the conventional wireless power transmission device 1 is operated in the charging mode, the above charging process is performed and not redundantly described herein. When the conventional wireless power transmission device 1 is operated in the detecting mode, the conventional wireless power transmission device 1 is electrically conducted to periodically generate the electromagnetic effect at a predetermined time interval (e.g. 100 ms) according to predetermined settings. Moreover, in the detecting mode, the conventional wireless power transmission device 1 judges whether the conventional electronic device 2 to be charged is placed on the main body 10 by detecting whether a communication signal is transmitted from the receiver coil 21 of the conventional electronic device 2. If the conventional wireless power transmission device 1 judges that the conventional electronic device 2 to be charged is placed on the main body 10, the operating mode of the conventional wireless power transmission device 1 is switched from the detecting mode to the charging mode. Under this circumstance, the conventional wireless power transmission device 1 charges the conventional electronic device 2 without the need of saving the electric power.
However, if the conventional wireless power transmission device 1 is operated in the detecting mode and the conventional electronic device 2 is not placed on the main body 10, some drawbacks may occur. Since no object is placed on the main body 10 to absorb the magnetic flux which is generated by the electromagnetic effect and the generated energy in a short time period is very large, the electromagnetic wave is scatted everywhere by radiation. As known, the scattered electromagnetic wave not only influences the electronic device but also hurts the user's body.
Therefore, there is a need of providing a wireless power transmission device for avoiding the generation of the scattered electromagnetic wave.